LVDS, which is standardized as IEEEP1596, 3, is used for transmitting a digital signal by changing the directions of a current flowing in a pair of resistor-terminated differential transmission lines, and is generally capable of transmitting the digital signals at high speed and with low power consumption and less noise.
A transmitting apparatus that is used in LVDS has a first output terminal and a second output terminal that are connected to a pair of differential transmission lines, wherein when a digital signal to be transmitted is at an H level, a current signal flowing from the first output terminal to the second output terminal via the pair of differential transmission lines is output, and when the digital signal to be transmitted is at an L level, a current signal flowing from the second output terminal to the first output terminal via the pair of differential transmission lines is output.
Incidentally, when performing high-speed, long-distance signal transmission, a problem arises in which the bit error rate obtained at the time of reception is increased due to attenuation of the AC component of a signal in the differential transmission lines. Specifically, when the level of a digital signal to be transmitted is inverted and thereby the directions of the current signals that are output from the first output terminal and second output terminal of the transmitting apparatus are inverted, it requires time for the magnitude of the current signals to reach a predetermined value after the inversion, and, as a result, a reception error easily occurs on the receiving apparatus side.
Patent Document 1 discloses an invention for solving such problems. The transmitting apparatus of the invention disclosed in Patent Document 1 has the magnitude of a current signal exceed the predetermined value during a certain time interval after inverting the direction of the current signal that is output from the first output terminal to the second output terminal, to thereby reduce the time required for the magnitude of the current signal to reach the predetermined value after the inversion.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2002-368600
The transmitting apparatus of the invention disclosed in Patent Document 1 has an active element for performing current control on a current source, and a passive element for performing voltage signal on a current sink, in order to have the magnitude of the current signal exceed the predetermined value during a certain time interval after inverting the direction of flow of the current signal. Since the transmitting apparatus performs both current control and voltage control, a problem arises in which the common mode potential fluctuates easily and EMI (electromagnetic interference) noise increases due to a phenomenon in which the current signal loops back via the differential transmission lines and terminating resistors.